1. Field
The present disclosure relates to an organic light emitting display (OLED) device, and more particularly, to an OLED being capable of preventing a brightness non-uniformity problem.
2. Discussion of Related Art
Recently, flat panel display devices, such as a plasma display panel (PDP), a liquid crystal display (LCD) device, and an OLED device, are widely researched and used.
Among these flat panel display devices, since the OLED device as a self-emission type display device does not require a backlight unit, the OLED device may have advantages of light weight and thin profile.
In addition, the OLED device has excellent characteristics of a viewing angle, a contrast ratio, power consumption, a response time, production costs, production yield, and so on.
The OLED device may include a switching thin film transistor (TFT), which is connected to gate and data lines, a driving TFT, which is connected to the switching TFT, and an organic emitting diode. The organic emitting diode is connected to the driving TFT and includes a first electrode, an organic emitting layer and a second electrode.
The first electrode may serve as an anode and may include a transparent conductive material having a relatively high work function. The second electrode may serve as a cathode and may include a metallic material having a relatively low work function. The metallic material may have an opaque property.
In a top emission type OLED device, the light from the organic emitting layer passes through the second electrode that is partially opaque. Accordingly, a thickness of the second electrode should be controlled such that the second electrode has a good light-transmissive property.
However, when the thickness of the second electrode is lowered, the resistance of the second electrode is increased such that a voltage drop problem in the second electrode is generated. Namely, a brightness non-uniformity problem in the OLED device is generated.
Particularly, the above brightness non-uniformity problem is serious in a large-size OLED device.
To prevent the above brightness non-uniformity problem, an auxiliary line, which is connected to the second electrode, may be formed to reduce the resistance of the second electrode.
FIG. 1 is a schematic plane view of the related art OLED device, and FIG. 2 is a schematic cross-sectional view taken along the line II-II in FIG. 1.
Referring to FIG. 1, the related art OLED device includes a substrate 11, which includes a plurality of pixel regions P, a first electrode 50 disposed on or over the substrate 11 and in each pixel region P, an auxiliary electrode 53 disposed at a boundary of the pixel region P and a bank 57 disposed at the boundary of the pixel region P. The auxiliary electrode 53 is spaced apart from the first electrode 50. The bank 57 covers the auxiliary electrode 53 and edges of the first electrode 50 and includes an auxiliary contact hole 55 exposing a portion of the auxiliary electrode 53.
The auxiliary electrode 53 and the auxiliary contact hole 55 have substantially the same width as the first electrode 50 and are separately arranged at each pixel region P.
Referring to FIG. 2, a semiconductor layer 13 including a first region 13a and second regions 13b at both sides of the first region 13a is formed on the substrate 11. The first region 13a is formed of intrinsic poly-silicon, and the second region 13b is formed of impurity-doped poly-silicon.
A gate insulating layer 15 is formed on the semiconductor layer 13, and a gate electrode 25 corresponding to the first region 13a of the semiconductor layer 13 is formed on the gate insulating layer 15. An interlayer insulating layer 17 is formed on the gate electrode 25.
In this instance, semiconductor contact holes 21 are formed through the gate insulating layer 15 and the interlayer insulating layer 17 to expose the second regions 13b of the semiconductor layer 13.
A source electrode 33 and a drain electrode 36, which are spaced apart from each other, are formed on the interlayer insulating layer 17. The source and drain electrodes 33 and 36 are electrically connected to the second regions 13b of the semiconductor layer 13 through the semiconductor contact holes 21, respectively.
The semiconductor layer 13, the gate electrode 25, the source electrode 33 and the drain electrode 36 constitute a driving TFT DTr.
A passivation layer 19, which may provide a flat top surface, is formed on or over the driving TFT DTr and over an entire surface of the substrate 11. A drain contact hole 43 exposing the drain electrode 36 of the driving TFT DTr is formed through the passivation layer 19.
The first electrode 50, which is connected to the drain electrode 36 through the drain contact hole 43, is formed on the passivation layer 19 and in the pixel region P, and the auxiliary electrode 53, which is spaced apart from the first electrode 50, is formed on the passivation layer 19 and at the boundary of the pixel region P.
The bank 57, which includes the auxiliary contact hole 55 exposing the auxiliary electrode 53 and covers edges of the first electrode 50 and the auxiliary electrode 53, is formed a the boundary of the pixel region P.
The bank 57 has a lattice shape to surround the pixel region P, and an organic emitting layer 60 is formed on the first electrode 50 in the pixel region P. In addition, a second electrode 70 is formed over an entire surface of the substrate 11 including the bank 57 and the organic emitting layer 60. As a result, the second electrode 70 is electrically connected to auxiliary electrode 53 through the auxiliary contact hole 55.
The first and second electrodes 50 and 70 and the organic emitting layer 60 therebetween constitute an organic emitting diode E.
Since the auxiliary electrode 53 is electrically connected to the second electrode 70, the sheet resistance of the second electrode 70 is lowered. As a result, the brightness non-uniformity problem can be prevented or minimized.
On the other hand, the organic emitting layer 60 may include a hole injection layer (HIL), a hole transport layer (HTL), an emitting material layer (EML), an electron transport layer (ETL) and an electron injection layer (EIL) sequentially stacked on the first electrode 50.
Each of the layers of the organic emitting layer 60 may be formed by a solution process or a deposition process. For example, since some materials for each layer of the organic emitting layer 60 has bad stability for the soluble process, the HIL, the HTL and the EML are formed by the soluble process and the ETL and the EIL are formed by the deposition process.
In addition, the blue emitting material does not provide the desired property by the soluble process. Accordingly, the blue emitting material pattern may be formed by the deposition process over an entire surface of the substrate 11. Namely, each of the HIL, the HTL, the red emitting material pattern and the green emitting material pattern is formed in each pixel region P by the solution process, while each of the blue emitting material pattern, the ETL and the EIL is formed over an entire surface of the substrate 11 through a deposition process.